1. Field of the Invention
The present invention relates to delivery systems for delivering and deploying medical devices such as stents. More specifically, the invention relates to a medical device delivery system having an outer sleeve, and a storage sleeve located between the outer sleeve and the medical device. The medical device may include all self-expanding catheter delivered prosthetics, including stents and IVC filters, or the like, including medical devices of utility in any body lumen, including the esophagus, urethra, ureter, biliary tract, blood vessels or other body lumens.
2. Description of the Related Art
Stents and delivery systems for deploying stents are a highly developed and well known field of medical technology. Stents have many well known uses and applications. A stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens.
The preferred present stent delivery apparatus may be utilized with any self-expanding stents, which are known in the art. A well known self-expanding stent is the woven braided stent disclosed in U.S. Pat. Nos. 4,655,771 (Wallsten); 4,954,126 (Wallsten) and 5,061,275 (Wallsten), although any type of self-expanding stent may be deployed using the inventive delivery system and method. A preferred stent for use with the stent delivery system of the present invention is described in co-pending PCT Application PCT/US95/06228 directed to "Improved Tissue Supporting Devices", incorporated herein by reference.
The delivery systems for stents are generally comprised of catheters with the stent axially surrounding the distal end of the catheter. It is highly desirable to keep the profile of the catheter as small as possible. Therefore, self-expanding stents are generally confined in a reduced radius for delivery to the deployment site. Once the stent is deployed the catheter is removed, leaving the stent implanted at the desired location to keep the vessel walls from closing.
A variety of techniques have been developed for holding a self-expanding stent in its reduced configuration while moving the distal end of the catheter to the deployment site. For example, in U.S. Pat. No. 4,655,771 (Wallsten), gripping members at either end of the stent hold the stent in an axially-elongated position, which causes the stent to take a reduced radius delivery configuration.
Another common technique for maintaining the self-expanding stent in a reduced radius delivery configuration is using a sheath which surrounds the stent and compresses it around the catheter. This technique is disclosed in U.S. Pat. No. 5,071,407 (Termin) and U.S. Pat. No. 5,064,435 (Porter), both of which use a silicon rubber sheath to compress the stent. A similar technique is disclosed in U.S. Pat. No. 5,026,377 (Burton) and U.S. Pat. No. 5,078,720 (Burton).
A variation on surrounding the stent with a sheath is disclosed in U.S. Pat. No. 4,732,152 (Wallsten); U.S. Pat. No. 4,848,343 (Walisten) and U.S. Pat. No. 4,875,480 (Imbert), all of which disclose using a sleeve formed of a doubled-over section of membrane to compress and contain the stent.
U.S. Pat. No. 5,234,457 discloses using a sheath to surround a mesh stent of the type disclosed in U.S. Pat. No. 4,922,405. However, in this patent the sheath is not used to compress the stent, but is used to prevent fluid from accessing the stent. The stent is impregnated with a pure gelatin or other dissolvable material which, when cured, has sufficient strength to hold the stent in its reduced delivery configuration. Once the sheath is withdrawn, the stent is exposed to the body fluids which dissolve the gelatin, allowing the stent to self-expand. This reference also discloses using axial distribution of gelatins with different rates of thermal decomposition to control the physical profile of the stent as it expands. However, using an impregnated mesh stent adds several inconvenient manufacturing steps to the process of preparing the stent for implantation.
In addition, none of the prior art methods of containing self-expanding stents address the problems associated with storage. For example, the outer sleeve of prior delivery systems can creep during storage and/or under elevated temperature conditions due to the expansion forces of the stent onto the inner diameter of the sleeve. As storage temperatures increase, for example, certain stenting materials such as nitinol, become stronger. Such a self expanding stent could conceivably expand during storage and not only deform the outer sleeve, but also become unsuitable for use due to its expansion.
There remains a need in the art for a stent delivery system in which the outer sleeve and the stent are retained in place for the purposes of storage, thereby preserving the shape of the stent and the sleeve. Furthermore, there remains the need for a stent delivery system in which the profile of the delivery catheter is retained in storage.